Re: object algebra

"Neo" <neo55592_at_hotmail.com> wrote in message news:4b45d3ad.0402280831.694afb96_at_posting.google.com...
> > > Color = {Red, green, blue, "Not Applicable", "Unknown"} [is a no, no]
> >
> > Closure doesn't have to do with the set, of course, but with the type -
> > you're talking about operations over relations. I don't think the set
above
> > has a problem with closure, though. Joins, projections, etc. which
reference
> > an EYE_COLOR attribute can do so meaningfully and without the
ambiguities of
> > nulls. Given proper type definition facilities, you can do whatever you
like
> > with the NOT_APPLICABLE value.
>
> Given the table:
> Person EyeColor
> ------ --------------
> Mary NOT_APPLICABLE
> Bob NOT_APPLICABLE
>
> Then, Mary.EyeColor equals Bob.EyeColor

No. You're free to define the domain and its operations as you wish. Received on Wed Mar 03 2004 - 14:13:12 CET